The main aim of this study was to determine the aromatic compounds in grilled beef samples from the Fleckvieh cattle breed. The bulls were assigned into three groups according to the nitrogen source in their feed ration – control group with urea supplementation, group with extruded rapeseed meal addition and group which received a feed ration enriched with lupine seed. Volatile substances were isolated using solid phase microextraction (SPME) and analysed by gas chromatography with mass spectrometry (GC-MS), and their odour activity was subsequently determined using olfactometry (GC-O). The highest average detection frequency was recorded for (E)-2-nonenal and (E,E)-2,4-nonadienal, which also had a relatively high odour activity. Among other significant substances detected in the samples are hexanal, heptanal and octanal. These aldehydes, which are responsible for the development of grassy and fresh/green taste and aroma in meat, had the highest detection frequency but the lowest odour intensity. The experiment revealed that the source of protein in the feed ration influenced the overall aroma of the meat. The inclusion of white lupine seed in the feed ration resulted in a reduction of the typical beef aroma and, on the contrary, an increase in the development of some abnormal odours that are negatively perceived by the consumers. Different chemical compositions are factors of importance for explaining the different aroma profiles between the groups, but some other parameters could also play an important role which needs to be paid attention to in the future research.